Columbium alloy separator



United States Patent 3,380,917 COLUMBIUM ALLOY SEPARATOR Raymond R. Boucher, Moodus, William J. Maynard, Higganum, and Bernard Sabo, Wallingford, Conn., assignors to United Aircraft Corporation, East Hartford,

Conn, a corporation of Delaware No Drawing. Filed Jan. 6, 1965, Ser. No. 423,871

4 Claims. (Cl. 25225) ABSTRACT OF THE DISCLOSURE A separating composition to minimize the metallurgical bonding between the canning material and the billet in the jacketed hot-working of metals consisting essentially of a reactive-refractory metal boride, such as titanium diboride, together with a refractory binder.

This invention relates in general to the hot-working of metallic materials and more particularly to means for minimizing metallurgical bonding between the canning material and the billet in the jacketed hot-working of metals. It contemplates a novel separating composition which may be readily applied to the surface of an ingot and/or a canning material to inhibit bonding therebetween.

In the hot-working of metallic materials which are particularly susceptible to detrimental atmospheric contamination at elevated temperatures, it is common practice to encase the billet to be worked in a protective sleeve or can before heating is undertaken. The jacketing method is most often employed where the heating and hotworking are to be performed without the benefit of a protective gas cover. However, even in those instances where the working may be done in vacuum or in an inert atmosphere, it is frequently advantageous to jacket the billet since, even in such cases, impurities present in the inert gas cover, or residual air in the case of vacuum operations, may be present in sufficient quantity to severely contaminate the product.

The jacketing method has found further utility in protecting the billet surface from mechanical damage during the various fabrication processes and it is frequently used for this purpose even though the billet material itself is not prone to surface oxidation. In the extrusion of soft alloys, a hard surface imperfection is often picked up by the die and dragged along the entire billet surface. This may be prevented by interposing a protective sleeve between the billet and the die. The protective sleeve will additionally forestall any unfavorable reaction between the billet material and the die material.

In still another application of the jacketing method, a sleeve of relatively high tensile strength is frequently utilized around a billet of lower strength to permit the billet to be successfully drawn. Further, in the extrusion of certain alloys a clad is used to prevent shattering or splintering of the billet upon the exertion of ram pressure.

Although not confined thereto, the separating composition and hot-working process described herein have found particular utility in the processing of the refractory metals which, in general, have a well-known low resistance to surface oxidation and internal hardening upon exposure to air at high temperatures. By means of the jacketing method, the critical processing procedures for such materials such as working temperatures, heat treatment temperatures, and working reductions, may be es tablished at their optimum levels irrespective of the surrounding atmosphere.

As used in this specification and claims, it will be understood that the term refractory metals has refer- 3,380,917 Patented Apr. 30, 1968 ice ence to those metals in Groups 11 and 12 of the Periodic Table, i.e., vanadium, columbium, tantalum, chromium, molybdenum, and tungsten and alloys thereof. The term reactive metals will be understood to have reference to those metals in Group 10 of the Periodic Table, i.e., titanium, zirconium and hafnium and their alloys. The term reactive-refractory metals will be understood to have reference to the metals in Groups 10, 11 and 12 of the Periodic Table as above enumerated.

Since the protective sleeve is usually intended to provide interim protection only and is not to be incorporated in the final product, it is removed from the billet subsequent to the hot-working operations. Stripping of the clad from the billet may be accomplished either by mechanical or chemical means, although it is frequently advantageous and the usual practice with respect to materials of high purity to mechanically strip the clad from the billet. Experience has demonstrated that, in the environment of high pressure and high temperature, a metallurgical bond is frequently developed between the canning material and the clad, sometimes referred to as solid-state Welding or diffusion bonding. When such a bond has been effected, the clad is not easily removed from the billet. Because of the solid-state bonding, it becomes difficult to ascertain the location of the interface between the two materials and it is, therefore, necessary to remove a portion of the billet surface to a considerable depth in order to remove all traces of the canning material. An expensive machining operation is therefore made mandatory and a considerable loss of valuable billet material is dictated.

It is an object of this invention to provide means whereby machining costs and material losses may be minimized in the fabrication of metallic materials in a jacketed hotworking operation.

It is a further object of this invention to provide means whereby the metallurgical bonding between metallic materials may be minimized.

A still further object is to provide a separating composition which may be interposed between a protective sleeve and the billet in the jacketed hot-working of metals to inhibit metallurgical bonding therebetween.

Another feature is the provision of a separating composition which may be easily applied to ingots and protective sleeves of any shape prior to jacketing of the ingot.

These and other objects of this invention will be apparent or will be pointed out in the following detailed description and should not be construed as limitations on the scope of this invention.

For maximum utility, a separating composition should completely prevent metallurgical bonding between surfaces to which it is applied. Additionally, it must be characterized by case of application, chemical compatibility with the materials with which it is in contact, and adherence after application to permit handling during the subsequent canning operation. Various compounds have been used for this purpose previously. Zirconium dioxide, applied to columbium alloys as an aqueous solution and subsequently dried, was tested as a separating material. Four columbium clad columbium alloy billets utilizing the zirconium dioxide separator were extruded. Two samples extruded at 2300 F. exhibited moderate clad-to-billet bonding and two samples extruded at 3100" F. exhibited extensive bonding. The zirconium dioxide coating, moreover, was characterized by poor adherence to the billet when dry and extreme care was required in the jacketing operation to prevent coating discontinuities. Further, it was demonstrated that bonding would occur despite the presence of an intact zirconium dioxide coating. It was quite evident that the zirconium dioxide separator did not have sufficient adherence to withstand the additional handling necessary before the coated billet was jacketed and ready for hot-working and further that, at the hot-working temperatures envisioned, the bonding was too extensive to permit easy removal of the cladding material.

Further experimentation revealed that titanium diboride interposed as a separating composition between a columbium alloy ingot and a columbium protective sleeve was effective in preventing metallurgical bonding therebetween at temperatures up to the melting point of the separating composition. Two clad samples utilizing the titanium diboride separator were extruded at 2300 F. and two sam ples were extruded at 3100 F. and, on a subsequent metallographic examination, it was ascertained that no bonding had occurred. This had been anticipated since the protective sleeve was easily peeled off the ingot after a rough machining operation and scoring of the sleeve to within 0.0100.0l of the ingot surface. in the initial test ing a limit of 3100" F. was established, not by the properties of the separating composition, but by the physical limitations of the test equipment. Subsequent experimentation, however, established the utility of this separator at temperatures up to its melting point.

Although the initial titanium diboride test work was oriented toward the development of a separating composition for use in the extrusion of the refractory metals and, more specifically, columbium and columbium alloys, further testing has revealed that its utility is not confined thereto. The separator performs equally well with all materials with which it is chemically compatible. Columbium clad with stainless steel has been successfully hot-rolled without bonding utilizing this separator. Similarly, various titanium and tungsten base alloy articles have been satisfactorily hot-worked with various cladding materials, including mild steel, with no visible bonding between the sleeve and the ingot.

Titanium diboride was originally selected as the basic material in the separating composition because of tita niums known ability to form a protective coating of its own upon exposure to oxygen. It was felt, therefore, that additional protection would be provided by the titanium coating in the event of a rupture of the clad during the fabrication process. It has been established, however, that metallurgical bonding between materials is inhibited by any boride or combination of borides from the group of metals comprising the reactive and refractory metal groups. In addition to the titanium diboride test work, borides of molybdenum and columbium were utilized satisfactorily as metallurgical bond inhibitors.

For ease of application of the titanium diboride to a billet surface it was found advantageous to form a paste therefrom by blending the titanium diboride powder with 5-40 percent by weight of a refractory binder such as titanium dioxide powder and adding to the resulting powder mixture sufficient water to form a viscous composition. The binding material in the initial test work, titanium dioxide, has been demonstrated not to directly contribute to the separating function. While titanium dioxide was selected as the binder because of titaniums known ability to form a coating of its own when oxidized and because of its compatibility with columbium, many other binders are equally satisfactory. In the selection of a binder the following characteristics must be considered and any binder possessing these characteristics may be utilized:

(1) chemical and metallurgical compatibility with the metallic materials,

(2) chemical compatibility with the separating compound,

(3) a melting point in excess of the desired hot-working temperature, and

(4) the ability to form a reasonably adherent coating when dry;

In addition to the preferred titanium dioxide binder, among the other refractory binders which will perform satisfactorily in this capacity are columbium oxide, beryllium oxide, aluminum oxide, zirconium dioxide, molybdenum diboride and vanadium diboride, The foregoing grouping is representative only and should not be construed as an exclusive listing.

It is quite obvious that in the formation of the paste from the mixture of boride and binder powders any volatile chemically-compatible liquid dispersant may be utilized. Its primary function is to adjust the separating composition to a consistency suitable for painting, spraying, or other means of application known to those skilled in the art and it is usually removed from the system by vaporization prior to jacketing of the billet.

Since the only purpose of the binding material is to provide means whereby the boride separating composition is held on the ingot surface, it is quite obvious that in the case of separators which are adherent in and of themselves no binding material need be added to the composition. It is further obvious that there is a practical limitation to the amount of the paste-forming composition that may be added to the overall separating compound mixture. Testing with titanium dioxide as a binder and titanium di boride revealed that if less than approximately 5 weight percent of the titanium dioxide was added to the separator, there was insufiicient binding of this separating composition to the billet surface to permit routine handling in accordance with normal shop practice. On the other hand, when more than about 40 weight percent of the binder was added to the separating composition, it tended to mask the effectiveness of the separator. Therefore, when the separating compound is not characterized by adherence in and of itself, a suitable binder must be added thereto normally in a ratio of from 5-40% by weight and preferably from 20-30% by weight. It will be understood, however, that although it is preferable to mix the separator with another powder to form an adherent paste for the purpose of convenience in shop handling, the paste-forming composition, since it contributes nothing to the separating function per se, may be dispensed with entirely in certain applications.

The separating composition is preferably formulated and applied by blending together fine powders of the boride separator and a refractory binder in a weight ratio of approximately 3 parts boride per 1 part binder. Suflicient water is added thereto to form a thick paste. The paste is then spread on the surface of the ingot to be worked over all surfaces with which the protective sleeve may come in contact. It has been demonstrated that the thickness of the wet layer thus applied is relatively immaterial as long as the surface coverage is complete. After the paste has been applied to the billet, the billet is dried, usually by permitting it to stand overnight, although the process may be hastened by heating or vacuum. The billet thus coated is then clad with the protective sleeve. For the sake of economy, sleeves of mild steel are frequently employed as the clad although other materials are equally suitable.

Articles prepared by this method utilizing this separating composition have exhibited no visible bonding between the part being worked and the clad, and the surface finish of the part after'hot-working has been free from surface imperfections resulting from the working process.

In many applications, after the part has been hotworked, the clad is removed and the part is subjected to further fabrication processes such as swaging, rolling and machining, but these are normally performed at ambient temperature where surface contamination normally is not a significant problem. Through utilization of this separating composition, it has been found unnecessary to machine the surface of the ingot between the hot-working and cold-working operations. Therefore, through practice of this invention expensive machining may be eliminated and material losses minimized in the fabrication processes.

Although this invention has been described with reference to specific chemical compounds and metallic materials, the invention in its broader aspects is not limited to the specific details described, and departures from such details will be obvious to one skilled in the art of metallurgy and metal fabrication processes within the scope of the appended claims Without sacrificing the advantages of this invention.

We claim:

1. A separating composition to inhibit solid-state bonding between metalli materials consisting of at least one boride selected from the group consisting of the reactive and refractory metal borides admixed with 5-40 percent by Weight of a refractory binder.

2. The separating composition of claim 1 wherein the boride is selected from the group consisting of titanium diboride, molybdenum diboride, and colurnbium diboride.

3. The separating composition of claim 2 wherein the refractory binder is selected from the group consisting of titanium dioxide, beryllium oxide, aluminum oxide, zir- 6 conium' dioxide, molybdenum diboride and vanadium diboride.

4. In a jacketed hot-Working of metallic materials, a separating composition to inhibit metallurgical bonding between the ingot and the clad consisting of essentially 60-95 Weight percent of titanium diboride and 5-40 Weight percent of titanium dioxide.

References Cite-:1

UNITED STATES PATENTS 3,161,595 12/1964 Fenker 25225 DANIEL E. WY MAN Primary Examiner.

CHARLES W. LANHAM, Examiner.

E. M. COMBS, Assistant Examiner. 

